DESCRIPTION: Traumatic brain injury (TBI) is a problem of epidemic proportions in both the United States and India. Outcomes following severe TBI, defined by a Glasgow Coma Scale <8, are much worse in India and most of the developing world than in the US. One possible reason for the discrepancy in outcomes may be the very limited use of technology to monitor intracranial pressure (ICP) in India. There is an urgent need for a noninvasive tool for the assessment of ICP. Raised ICP results in distension of the optic nerve sheath (ONS), a continuation of the dura. Ocular imaging, performed by clinicians using widely available point-of-care ultrasound machines, can be used to detect ONS distension a fixed distance behind the eye. A study conducted by the PI at the University of Michigan identified an Optic Nerve Sheath Diameter (ONSD) cutoff of >0.51cm as having 98% sensitivity and 91% specificity for the detection of intracranial hypertension, defined as ICP>25mmHg. There is significant variation in the optimal ONSD threshold to detect raised ICP, likely because of variations in the population studied and measurement technique. The optimal ONSD to identify elevated ICP in the Indian population is not known. More importantly, the ability of ONSD measurement to predict the more clinically meaningful endpoints of need for therapeutic intervention and risk of death has not been studied in any part of the world. Objectives: The primary aim of our study is to determine the optimal optic nerve sheath diameter (ONSD) measurement for the detection of raised intracranial pressure (ICP) when used as a screening test following severe traumatic brain injury in India. The secondary aims will be to evaluate whether optic nerve sheath diameter predicts Therapeutic Intensity Level and mortality following severe traumatic brain injury. Methods: This will be a prospective study at All India Institute of Medical Sciences (AIIMS), New Delhi, of the ability of ONSD measurement, performed by bedside clinicians at the time of admission and every 8 hours for 1 week following injury, to detect ICP>25mmHg on simultaneous gold-standard invasive monitoring. We will also assess the ability of ONUS to predict the need for higher levels of therapeutic intervention directed at control of ICP using the Traumatic Brain Injury Therapeutic Intervention Level (TIL) scale. The optimal ONSD for detection of elevated ICP in Indian patients will be identified using Receiver Operating Characteristic (ROC) curves, with emphasis on a cut-off with high sensitivity and acceptable specificity, as appropriate for a screening tool. The ability of the maximum ONSD value in the first 48 hours to predict TIL will be evaluated with covariate adjustment for age, gender, and relevant comorbidities. A secondary analysis will be performed to evaluate the ability of the highest ONSD measurement in the first 48 hours to predict mortality.